pf: fix pfi_ifnet leak on interface removal

The detach of the interface and group were leaving pfi_ifnet memory
behind. Check if the kif still has references, and clean it up if it
doesn't

On interface detach, the group deletion was notified first and then a
change notification was sent. This would recreate the group in the kif
layer. Reorder the change to before the delete.

PR: 257218
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D37569